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Galileo spacecraft passed within 363 miles of icy Europa, one of the sixteen moons of the planet Jupiter. Yesterday, scientists showed some of the pictures from that fly-by and said they may reveal a global ocean of water or slush lying under the broken ice that covers Europa's surface. The scientists said where there is water, there could also be life.

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JIM LEHRER: Finally tonight the secrets of Europa and to Elizabeth Farnsworth.

ELIZABETH FARNSWORTH: On February 20th, the Galileo spacecraft passed within 363 miles of icy Europa, one of the sixteen moons of the planet Jupiter. Yesterday, scientists at NASA's jet propulsion laboratory in Pasadena, California, showed some of the pictures from that fly-by and said they may reveal a global ocean of water or slush lying under the broken ice that covers Europa's surface. And the scientists said where there is water, there could also be life. And here to tell us about Europa is Michael Carr, a planetary geologist who coordinates the planning of Galileo's picture-taking, and Torrence Johnson, the Galileo mission's chief scientist. Thank you both for being with us.

Mr. Johnson, explain the context of these pictures for us. Galileo's been exploring Jupiter and its moons for two years, right?

TORRENCE JOHNSON, Galileo Project Scientist: (Pasadena, CA) Approximately a year and a half now.

ELIZABETH FARNSWORTH: And what did you see in these pictures? It's been taking pictures of Europa all the way along. What did you see in these pictures you hadn't seen before?

TORRENCE JOHNSON: Well, the last two encounters that we had were very close to Europa, and not only did we get very high resolution pictures but we got lucky. Luck helps in science, as it does in other things, and we saw some very interesting places--in particular, this area where there appear to be ice rafts. And what I find most interesting—

ELIZABETH FARNSWORTH: But wait a minute. Let's put up--we have a picture that's called Europa Ice Rafts. Let's put it up. What do you mean "rafts," first of all?

TORRENCE JOHNSON: Well, I think one of the things that I find fascinating about this picture is you really don't need to be an expert in satellite photo interpretation to see what's going on. You're looking at an area about 25 miles across, and you're looking at a brittle, cold ice crust, which has clearly been broken up, and pieces have floated away from the edges of the areas where they've broken off from, very similar to what you see in Arctic areas on the Earth. And a kid in school could look at those striations on the surface which are soft of pressure ridged type things and put the jigsaw puzzle back together and convince themselves that it had mile-sized blocks of icebergs or rafts, if you will, that broke away from the edge and floated and moved along that surface. And that implies that there was liquid water under there at that time.

ELIZABETH FARNSWORTH: So, Mr. Johnson, is it sort of like what happens in the Arctic Ocean when the ice breaks up?

TORRENCE JOHNSON: Yes, in fact, this--this looks very much like that. The geologists that have been studying this and, in fact, at our briefing yesterday we even had an expert in Arctic ice engineering, and he compared this directly with some of the types of things one sees in the Arctic.

ELIZABETH FARNSWORTH: Okay. Mr. Carr, you're one of the geologists. Tell us what you know about this ice, how deep it is. What--and why you surmise there may be water underneath it, because you don't know for sure, right? Let's get that clear.

MICHAEL H. CARR, United States Geological Survey: (San Jose, CA) We don't know for sure. But we can tell how deep it is because if, indeed, it is water and these are ice blocks floating in water, then it's very similar to icebergs on the Earth. And we can tell how deep it is by--how deep these extend by how far they poke up above the surface. And it looks as though the water--when this--these--this rafting took place--is about a kilometer below the surface.

ELIZABETH FARNSWORTH: Go ahead. Sorry.

MICHAEL H. CARR: About a little over half a mile. Now you asked how could there be water down there. Well, it had actually been predicted that there could be water below this icy crust. And the reason is that Europa's orbit is not exactly circular. It moves in and out with respect to Jupiter, and that causes flexing, flexing of the body. And this generates friction. And that keeps the ice melted at the bottom of the icy crust.

ELIZABETH FARNSWORTH: That's what's producing the heat that keeps it melted?

MICHAEL H. CARR: Exactly.

ELIZABETH FARNSWORTH: And could anything else be causing the breaking up of the ice? Apparently, the gravity works in a way that could do it too, right, or no?

MICHAEL H. CARR: Well, that's unlikely because this is a very flat area, so these are not simply blocks that are moving down slopes. There has to be traction from below, and the only--things have to be moving down there. And if they're moving, they're essentially liquid.

ELIZABETH FARNSWORTH: Okay. Mr. Carr, we're going to put up another picture called "Ridges, Hills, and Domes." Tell us if there's anything else in this picture that we should be thinking or knowing about.

MICHAEL H. CARR: I mentioned that--that this flexing of the crust is--is generating the heat. And we can see evidence of that flexure in these pictures because these ridges cover the entire body. And they're in some way caused by this constant movement to the surface that's by--that's generated by Europa moving in and out in its orbit around Jupiter.

ELIZABETH FARNSWORTH: Mr. Johnson, can you see a water line at all?

TORRENCE JOHNSON: Well, we've been speculating on that. It has to do with the same argument that Mike Carr just mentioned about the icebergs, is that the thickness is this brittle layer where we see these disrupted areas, seems to be fairly constant in many of the places we see it, which suggests that at the time that this heating occurred, which we believe to be fairly recent in the geological past, the water was literally only a few miles below the surface over most of the region we looked at here. I should emphasize that we've only looked at a tiny fraction of the surface of Europa at this resolution, so we're very excited about the prospects of looking at other areas and comparing them with the things we're seeing here.

ELIZABETH FARNSWORTH: Mr. Johnson, what's it like up there? What's Europa like? Is it cold? Is it dark?

TORRENCE JOHNSON: The sun is about 25 times less powerful than it is here on the Earth, but it's still pretty bright, however. But the surface reflects light very well at Europa, as well as being further away from the sun. The end result of that is that this nearly airless surface of Europa at the very surface is extremely cold, approximately minus 173 degrees Centigrade. That's very cold, and the ice at the surface acts like rock. And that makes it all the more remarkable, if you will, this tidal heating and friction that Mike Carr was discussing has actually caused it to melt at a relatively shallow depth.

ELIZABETH FARNSWORTH: Mr. Carr, even in this very cold world there could be life, right? I know that nobody can say, but could there be?

MICHAEL H. CARR: Well, that's why we're so excited about the possibility of there being an ocean there. Biologists have found the most primitive life forms on Earth, the bottom of the Earth's ocean at volcanic vents, and a number of biologists believe that's where life started on Earth. Well, on Europa we have an ocean there that's probably warming, particularly early in the planet's history there were probably volcanic vents on this ocean floor, and so it raises the possibility that life could have started there also. There's no light penetrating through this icy crust. It's very dark down there, but these primitive organisms that live at the volcanic vents on our ocean floor live--they don't live off of light; they live off chemicals that are brought up to the surface by the volcanic activity. And the same thing could happen there. So yes, it's exciting.

ELIZABETH FARNSWORTH: And, Mr. Carr, how would you find out? What do you have to do to find out whether there is water and then perhaps life?

MICHAEL H. CARR: That's right. The first step would be to really do experiments to confirm that, indeed, the water is there and it's fairly close to the surface. And then if that turns out to be the case, we could probably have missions there, landed missions, that might have thrown up--look at say an impact crater, a crater there where material has been thrown up onto the surface, or some of these places where water has come to the surface and sample it and look and see what's in the water.

ELIZABETH FARNSWORTH: Mr. Johnson, put this possibility of life in the context of the other discoveries recently--the meteor from Mars that had some markings that indicated maybe they were the result of some sort of microbial life form. I may not be saying that right. Compare those, and put this in context for us. I just--I want to say one scientist we talked to said he's more excited than he's been in 30 years about what's he doing because of this.

TORRENCE JOHNSON: I think following on one of the points that Mike Carr just made is that the exploration of the environments where life is possible has exploded here on the Earth during a period of time when we've also been exploring our solar system. The types of hydrothermal microbial colonies, bacterial colonies that Mike Carr was just describing on the Earth's sea floors, were unimagined 30 years ago; that you could have life in those environments, which are actually very hot and because of volcanic energy. So the context to me is that here on Earth we're beginning to recognize very clearly that life can exist in very extreme environments well beyond what we used to think was conducive to life and may even have originated in some of these environments. Simultaneously, we're beginning in our exploration of the solar system to see other places where we might have environments that are similar to that which were--where these things exist on the Earth. So we're kind of moving out of our comfort zone, as you will. When I was in school many years ago, it was thought more or less absolutely that the only place life could exist in the solar system was in the sort of comfort zone right at the Earth's distance from the Sun--

ELIZABETH FARNSWORTH: I have to--

TORRENCE JOHNSON: --where you could have liquid water at the surface.

ELIZABETH FARNSWORTH: I have to interrupt you.

TORRENCE JOHNSON: And we're finding that's not necessarily true.

ELIZABETH FARNSWORTH: Sorry to interrupt you. We have to go, but that was fascinating. Thank you both very much.

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